Voltage Drop Issue

T

Tav1980

Member
Location
MD
Occupation
Electrical
Hello!

I’m at a house where the homeowner is reporting that the lights throughout the entire home dim significantly whenever appliances with motors—like the garbage disposal, dishwasher, or sump pump—kick on.

I hooked up my meter and observed a major voltage imbalance when the sump pump started: one leg dropped as low as 90V while the other spiked up to 150V. I saw similar readings when testing the dishwasher and garbage disposal. I isolated the panel by turning off the main, and I’m reading a proper 120/240V at the service entrance.

The issue only appears when a load involving a motor is started, and it causes other devices in the house to malfunction. The panel itself looks fine—no loose connections or obvious damage.

Has anyone encountered something like this? I know minor voltage drops under load are normal, but this seems excessive. I’m starting to suspect a problem upstream from the panel, possibly an issue with the service neutral.

Any thoughts or experiences would be greatly appreciated.

Thanks in advance!
 
When you see one line go up and the other down, it’s very likely to be a neutral issue. Where, is going to take some troubleshooting, but if you are seeing it on multiple different circuits in the house, it’s probably upstream from the MCB.
 
Tav1980 said:
Bad neutral it is. Thanks for everyone's input.
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Ignore the following if you have already diagnosed this as a POCO neutral issue and they have corrected it.

If not...

If you do get the POCO onsite – a classic failure on their part is to pull the meter and measure voltages. And they declare all is good on their side and leave. Naturally, with the meter out and no current flowing, the weak neutral problem is not seen at all. Either show them some of your testing at the main panel with widely varying L-N voltages, or ask them to load the service themselves. A good lineman will have a “Beast of Burden” tester on the truck and know how to use it.

Good luck.
 
MD Automation said:
If you do get the POCO onsite – a classic failure on their part is to pull the meter and measure voltages. And they declare all is good on their side and leave. Naturally, with the meter out and no current flowing, the weak neutral problem is not seen at all. Either show them some of your testing at the main panel with widely varying L-N voltages, or ask them to load the service themselves. A good lineman will have a “Beast of Burden” tester on the truck and know how to use it.

Good luck.
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I've had to "strongly" suggest that the lineman get in the bucket and go up by the transformer after he said everything looked fine at the meter. I put some big loads on the service and lo an behold he sees sparks on the neutral connection. He proceeds to fix while grumbling about his co-worker that had worked on it the month before.
 
MD Automation said:
Ignore the following if you have already diagnosed this as a POCO neutral issue and they have corrected it.

If not...

If you do get the POCO onsite – a classic failure on their part is to pull the meter and measure voltages. And they declare all is good on their side and leave. Naturally, with the meter out and no current flowing, the weak neutral problem is not seen at all. Either show them some of your testing at the main panel with widely varying L-N voltages, or ask them to load the service themselves. A good lineman will have a “Beast of Burden” tester on the truck and know how to use it.

Good luck.
Click to expand...
Officially known as the SuperBeast or the MegaBeast.

Mark
 
I ran into this in a house. Bad neutral and current flowing through the water pipe. POCO came out and plugged in the "beast" and declared everything fine and they had pulled the GEC off the water pipe temporally to prove the neutral is good but we still had amps on the water pipe.

I said "hold on" the house was wired in BX. If the BX was contacting the water pipe (like at a electric WH) you would still have a connection which it did. They re worked several neutrals on this house and other houses in the area and the amps on the water pipe dropped but not to 0.

In fact with the service to the house I was working shut down and the GEC disconnected the water pipe still had some amps.

Power from the neighbors coming in the water pipe through the BX armor to the panel and back on the neutral to poco trans

Or " How your neighbor can burn your house down"
 
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